Why do shave biopsies and punch biopsies used to diagnose suspected facial basal cell carcinomas measure a few mm instead of being below 1mm?

Question

Given a neoplasm of uncertain behavior of skin on a patient's face that is suspected to be a basal cell carcinoma (BCC), the typical first step is to perform a shave biopsy to determine the type of basal cell carcinomas so that one can decide the treatment {1}. Punch biopsies are also sometimes used instead of shave biopsies {2}.

Shave biopsies and punch biopsies used to diagnose suspected BCCs measure a few mm {2}. The downside of such shave or punch biopsies is that they leave a small scar.

Why do shave biopsies and punch biopsies used to diagnose suspected facial basal cell carcinomas measure a few mm instead of being below 1mm to avoid visible scarring? Of perhaps I am mistaken and there does exist biopsies to diagnose suspected facial basal cell carcinomas that avoid visible scarring?

I don't think we need to get over 1mm of cells for a histology to determine whether a neoplasm of uncertain behavior of skin is a BCC, and if it is, the BCC type, since a human skin cell is much smaller than 1mm.

---

References:

• {1} Medscape (mirror):

  A skin biopsy is often required to confirm the diagnosis and determine the histologic subtype of basal cell carcinoma (BCC). Most often, a shave biopsy is all that is required. [Mar 2, 2020]

• {2} https://www.apma.org/files/Derm-%20case%20reports%20APMA%202018.pdf (mirror):

  

Answer 1

A basal cell carcinoma (BCC) may have more than 1 subtype: if the biopsy is too small, the histopathologist may miss a subtype.

From {1}:

More than 26 different subtypes of BCC appear in the literature, but the more common, distinctive, clinicopathologic types include: nodular, micronodular, superficial, morpheaform, infiltrative and fibroepithelial (also known as fibroepithelioma of Pinkus). Combinations of these types can occur as well. The majority of BCCs are amelanotic, but variable amounts of melanin may be present within these tumors.

Missing a BCC subtype might result in deleterious consequences, e.g. one wouldn't want to treat a BCC with Imiquimod cream thinking that it is just a superficial BCC while it is in fact infiltrative.

---

References:

• {1} https://www.ncbi.nlm.nih.gov/books/NBK482439/